Vulcanization of rubber



Patented Apr. 1, 1952 VULCANIZATION RUBBER Rutherford 13.. Hill, Nitro, W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Original application September 24,

1947, Serial No. 775,959. Divided and this application September 19, 1949, SerialNO. 116,613

The present invention relates to new compositions of matter and more particularly to accelerators and curatives for the vulcanization of a rubber or a rubber containing material. In addition,

the invention relates to the process of vulcanizing alkaline eart me a hydroxides. o a rubber and to the vulcanized rubber products tgfitmc bases. P f rably rglanic bases stigon er obtained with the aid of the new accelerators. an ammonia such as cyc ohexy amin enZyl 'Ihiazole sulfides are widely used accelerators m D per e, ethyl amine, diet y amine, in the manufacture of rubber articles. For exmethyl amine. m yl amine. m phe ample, 2,2 dithio bis benzothiazole is a useful e yl ycl hexylami end the like y he accelerator but it is a high meltingsolid difficult u e A small amount o he base is sufiicientto disperse in a rubber and has a very objection- I n ra fg-1 1% based On th total Weight able tendency to cake on the roll and adhere gf ty e go poslt o is t s a torw For example. thereto; Lagenbeck and Rheim, Kautschuk, 12, o o mo added to a fusion m e o pp. 156-159 (1936) have demonstrated that fusion qual i i s by wei ht r sulfuranddithio bi of a thiazole sulfide and sulfur lowers the meltenzo iazo e a a d s d e p oduct ing point of the former sharply. Investigation melting at 011 e Other a es tha of these compositions revealed that incorporation had hellotieeehle effect p o ed 0 t into the rubber could be accomplished much more products Whwh were not grindable- In most quickly and easily than with the pure thiazole ie y vie t t 0f he a is bou h sulfides. On the other hand, the physical prop- 0p Imum c ra ion of baseerties of the fusion products from the standpoint The proportion sulfur can. vary widelyof shipping, handling, removing from th Ccigipositiotnskcontaming less than 50% sulfur aretainer, etc. were so objectionable asto preclude S0 and 8 ie y. and trea me ith a base de-i their use as commercial accelerators. They ar presses the melting point ti 1 e h soft sticky pastes at room temperatures. they hquefy at temperatures o s i above An object of this invention is to provide accelroom temperature a h e e e be easily crating compositions which may be quickly and gated i hamliled as j t It 15 preferred, uniformly incorporated into a rubber. A more owever emp composi ions Containing particular object of the invention is to provide ac- 3 least 50% Sulfur- These compositions are h celerating compositions which either melt or z d treatment witha b e a1- soften during the processing of the rubber. Any 50 en and qu y at h te pera other object is to provide thiazole accelerators in eS rea he during processing of e rubber- 7 improved physical form. A particular object is to The table below shows the irififience of v r in improve the physical properties of fusion prodthe proportion of dithio bis benz othiazolei-and nets of thiazole sulfides and sulfur. Other and sulfur, either in the presence or absenceof 'am further ob ects will in part be apparent and in monia. Fusion products were prepared in which gart piart1c1] ila1rly pointed out in the detailed the gram atoms of sulfur per gram mol of disulescnp ion 0 owing. fide were 16, 14, 12, 10.4, 10, 8, 6.9, 6, 4, 2.6 and 2 In accordance with the present invention it 40 respectively. Fusion was carried out by heating fiiiggstbgegi cgilscoveiredj thattigeatriientlgfdcompoisite til ingredients until a clear melt was obtained. u 1 pro uc s o lazo e su e acce ere compositions were cooled and then placed on igtigggglhvivlgh allojjlerproviideslfow nlielt'lilng g stezgnz1 bath and their physical condition at 95 c q an uni orm y 15- .no e he reparation of the fusion rod t perse into rubber at processing temperatures and was then repe ted, but in this case tlierel tv a 'at the same time possess satisfactory physical added to the melt 0.5% based on the total eem'- properties at room temperature. The base may be position of 28% ammonium hydroxide. Thefu added pllOl to during, or after the fus on. 7 sion mixtures were then allowed. to cool, their While chemical reaction between thiazole sulphysical condition noted and their melting points fides and sulfur has been postulated, this invention is not limited to any theory of the presence or absence of chemical modifications. The accelerating'properties of the fusionp'roducts areclosely 9 Claims. (Cl. 260-485).

comparable to that whichwouldbe expected from their thiazole sulfide content.

Apparently the nature of the, base employed is not critical.

determined. All of the compositions treated with ammonia and which contained at least 50% sul fur were hard friable products at room temperature. 4', I

The alkali metal hydroxides, the

Table I Without ammonia-Physical Alter ammonia Treatcondition of fusion product mentPhysicaT Con- Ditbio bis Sulfur atdition atbenzothiazole Per Per Cent Cent Room 'Iem- .0 C Room tem- M. P. perature perature C.

60.7 soft sticky..- solid liquid 104 51.5 a d 101 53.6 100 50.0 108 49.0 01 43.5 50 40.0 40 36.6 4': 27.8 43 20.0 44 10.2 40

While any base appears to accelerate thew Table III hardening, there is some variation in their effectiveness. For example, equal amounts by weight Modulus of Elastlcity Cure in lbsjinfiat elongaof d1th1o blS benzothiazole and sulfur were "tool Time Hons 'lB 3IlSi1l{Li8t Eli'ltimaite b I heated to form .a clear melt and then treated 5 lb sjini 2251 with 0.25% based on .the .total combined weight 300% 500% of. the following bases. The compositions were 05 then cooled and their physical properties noted. 1.. 00 123 100 850 2 15 15c 106 243 090 1 283 523 680 720 T 1 11 i 22' 21 1 3 1 3%? 1 221 m e 0. 580 a 9 45 453' 986 11600 130 30 1 a as 121% 1222 .Base Condition after cooling n l Stocks were com ounded com risin None softsticky. p p g NaOH. gtabeconbiing lhardandbrittleaiter48hours. NHa.- r and ritt c. Piperidine Do. Pmby weigh Cyclohexylaminc. Do. Stock Smokeggheot rubber 100 100 p nco e 5 into a container of .su1table capacity fitted 40 Carbon black" 4g withtan agitator there was charged .125 pounds Steario acid 3 3 of sulfur. The sulfur was melted and then 125 g i g 55 pounds of 2,2 dithio bis benzothiazole was added Ncyclohexyl2-benzothiazole 0.3 0.3 at 110-1l2 C. over a period :of about 40 minutes 0. 45 while stirring. The mixture was then heated to 0 148 C. and 5 pounds of a 25% aqueous caustic soda solution added gradually. The temperature dropped to 124 C. as the water evaporated but was then gradually brought up to 138 C. About minutes was required for the addition of the caustic and heating to 138 C. The melt was then poured out into pans and allowed to cool. After 18 hours the material had hardened considerably and after 48 hours was hard and brittle The stocks were milled at 95 C. at which tern.- perature Accelerator A softened and dispersed readily into the rubber whereas 2,2 dithio ibis benzothiazole tended to cake on the rolls instead of going into the rubber. The compounded stocks were cured in the usual manner by heating in a press for different periods of time at 144.5 C. The physical properties of the cured rubber products are set forth below:

so that it could be finely pulverized. The pulverized product is identified as Accelerator A in the Table IV stockbelow.

Stocks were compounded comprising: Modulus of Elasticity gum in lbs/lnflat elonga- Tensile at Ultimate Stock fi ions of Break in Elongation lbsJln. Percent Mins. Part by weight 300% 500% Stock I 1 2 15 1,000 l 2, 430 3, 840 600 15 045 2, 400 4, 110 705 30' 1, 450- a, 240 4,480 050 GR s'rubber 100 30 1,420 3.180 4, e40 050 Carbon black" 40 40 45 1, 595 3, 380 4, 350 000 Zinc oxide--- 3 45 1, 540 a, 440 4, 360 010 r 2. 0 0. 5 e0 1, 700 3, 4, 220 570 131mm bis benzothiazole.- 1. 5 00 1, 065 3, 300 4, 240 000 Accelerator A 3.0

The stocks so compounded were vulcanized by heating in a press for difierent periods of time at 142 C. The physical properties of the cured products are set forth in the table following.

Into a container of suitable capacity there was charged 39.3 parts by weight of 2,2 dithio bis benzothiazole and 60.7 parts by weightof sulfur. The mixture was heated until a clear melt was formed and then 0.5 part by weight of '28 ammonium hydroxide added, and the melt allowed to cool to room temperature. A hard grindable solid was formed designated as Accelerator B in the following stocks:

Part by weight Stock GR-S rubber 100 100 Carbon black 40' 40 Zinc oxide 3 3 Hydrocarbon softener 8 8 Sulfur 2. 22 O. 5 2,2 dithio bis benzothiazole. l. 18 Accelerator B 3. 0

Accelerator B melted on the bank of the stock during mixing. The compounded stocks were cured by heating in the usual manner for different periods of time at 142 C. The physical properties of the cured products are set forth below: C

1 No cure.

The accelerating compositions of this invention are useful in the vulcanization of sulfur vulcanizable rubbery materials generally. Suitable rubbers comprise india rubber, reclaimed rubber, balata, gutta percha, butadiene-1,3 polymer, copolymer of butadiene-1,3 and styrene, copolymer of butadiene-LB and acrylonitrile, and other sulfur vulcanizable rubbery products Whether natural or synthetic.

The present invention is not limited to the specific examples herein set forth of the preparation and use of the preferred accelerators. The procedure for the preparation of the fusion products may be varied as will be apparent to those skilled in the art to which the invention pertains. While the use of the new accelerators has been described by references to particular formulations, other ratios of the compounding ingredients than those mentioned in the examples as Well as other well known fillers, pigments, and the like may be employed in the. production of various types of rubber compounds. Where desired basic activating accelerators may be employed in conjunction with the fusion products, as for example diphenyl guanidine, dio-tolyl guanidine, thiocarbanilide, hexamethylene tetramine, para phenylene diamine, anhydro formaldehyde aniline, diphenyl guanidine phthalate, triphenyl guanidine, butylaldehyde aniline, dibutyl amine oleate and dicyclohexylamine oleate.

While sulfur may be added in addition to that present in the fusion product, the ratios in which the sulfur and accelerator are fused may be varied so as to avoid the independent addition of either ingredient. For example, in compounding a stock calling for 3 parts of sulfur and 1 part of 2,2 dithio bis benzothiazole, the sulfur and accelerator may with advantage be replaced by 4 parts of a fusion mixture of 3 parts of sulfur and 1 part of 2,2 dithio bis benzothiazole treated with a base as described herein. Thus, the invention contemplates replacing the usual sulfur and thiazole sulfide combinations with preformed composite fusion products fused in any of the ratios these ingredients are separately employed.

Instead of 2,2 dithio bis benzothiazole other thiazole sulfide accelerators may be fused with sulfur, as for example 2,2-dithio bis 4,5-dimethyl thiazole, 2,2-dithio bis ll-ethyl thiazole, 2,2- dithio bis 4-phenylbenzothiazole, 2,2-dithio bis methylbenzothiazole, 2,2-dithio bis G-phenylbenzothiazole and 2,2-dithio bis chlorobenzothiazole. .7

This invention is a division of co-pending application Serial No. 775,959, filed September 24, 1947, now'Patent No. 2,567,710, issued on September 11, 1951, and is limited solely by the claims attached hereto as part of the present specification.

What is claimed is:

1. The process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a composition prepared by treating with 0.1 %l.0% by weight based on the total composition of a base the composite heat fusion product of a 2,2-dithio bis thiazole and sulfur containing from 2 to 16 atomic weight proportions of sulfur per molecular proportion of said thiazole.

2. The' process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1 %-1.0% by weight based on the total composition of a base the composite heat fusion product of a 2,2-dithio bis arylenethiazole accelerator and sulfur containing from 2 to 16 atomic weight proportions of sulfur per molecular proportion of said thiazole.

3. The process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1%- 1.0% by weight based on the total composition of a base the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur containing from 2 to 16 atomic weight proportions of sulfur per molecular proportion of said thiazole.

4. The process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1 1.0% by weight based on the total composition of a metal hydroxide the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur, the proportion of sulfur by weight being at least equal to that of the 2,2-dithio bis benzothiazole but not more than about 60.7% of the total composition.

5. The process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1%- l.0% by weight based on the total composition of an alkali metal hydroxide the composite heat fusion product of 2,2-dithio bis benzothiazole and sulfur containing from 2 to 16 atomic weight proportions of sulfur per molecular proportion of said thiazole.

6. The process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1 1.0% by weight based on the total composition of ammonia the composite heat fusion product of 2,2'-dithio bis benzothiazole and sulfur, the proportion of sulfur by weight being at least equal to that of the 2,2'-dithio bis benzothiazole.

7. The process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1%- 1.0% by weight based on the total composition of an organic base the composite heat fusion product of 2,2'-dithio bis benzothiazole and-sulfur containing from 2 to 16 atomic weight proportions of sulfur per molecular proportion of said thiazole.

8. The process of vulcanizing a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1%- 1.0% by weight based on the total composition of an amine stronger than ammonia the composite heat fusion product of 2,2'-dithio bis benzothiazole and sulfur, the proportion of sulfur by weight being at least equal to that of the 8 2,2'-dithio bis benzothiazole but not more than about 60.7% of the total composition.

9. The process of vulcanizing' a sulfur vulcanizable rubber which comprises heating the rubber having incorporated therein a small amount of a composition prepared by treating with 0.1% 1.0% by weight based on the total composition of a base the composite heat fusion product of substantially equal proportions by weight of 2,2'-clithi0 bis benzothiazole and sulfur.

RUTHERFORD B. HILL;

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,544,687 Sebrell July '7, 1925 1,926,740 Clapson et al Sept. 12, 1933' 2,087,200 Clifford July 13, 1937 OTHER REFERENCES Kautschuk, V01. 12 of 1936, pages 156-159 

2. THE PROCESS OF VULCANIZING A SULFUR VULCANIZABLE RUBBER WHICH COMPRISES HEATING THE RUBBER HAVING INCORPORATED THEREIN A SMALL AMOUNT OF A COMPOSITION PREPARED BY TREATING WITH 0.1%-1.0% BY WEIGHT BASED ON THE TOTAL COMPOSITION OF A BASE THE COMPOSITE HEAT FUSION PRODUCT OF A 2,2''-DITHIOBIS ARYLENETHIAZOLE ACCELERATOR AND SULFUR CONTAINING FROM 2 TO 16 ATOMIC WEIGHT PROPORTIONS OF SULFUR PER MOLECULAR PROPORTION OF SAID THIAZOLE. 